body{
    padding: 0;
    margin: 0;
    font-family: sans-serif;
    background: url(../bg.jpg);
    background-attachment: fixed;
    background-position: center;
}
header{
    position: absolute;
    top: 0;
    left: 0;
    padding: 0 100px;
    background: #262626;
    width: 100%;
    box-sizing: border-box;
}
header .logo{
    color: #fff;
    height: 50px;
    line-height: 50px;
    font-size: 24px;
    float: left;
    font-weight: bold;
}
header nav{
    float: right;
}

header nav ul{
    margin: 0;
    padding: 0;
    display: flex;
}

header nav ul li{
    list-style: none;
}
header nav ul li a{
    height: 50px;
    line-height: 50px;
    padding: 0 20px; 
    color: #fff;
    text-decoration: none;
    display: block;
}

header nav ul li a:hover, 
header nav ul li a.active{
    color: #fff;
    background-color: #2196f3;
}

.menu-toggle{
    color: #fff;
    float: right;
    line-height: 50px;
    font-size: 24px;
    cursor: pointer;
    display: none;
}

@media(max-width: 900px){
    header{
        padding: 0 20px;
    }
    .menu-toggle{
        display: block;
    }
    header nav{
        /* display: none; */
        position: absolute;
        width: 100%;
        height: calc(100vh - 50px);
        /* height: 100vh; */
        background-color: #333;
        top: 50px;
        left: -100%;
        transition: 0.5s;
    }
    header nav.active{
        left: 0;
    }
    header nav ul{
        display: block;
        text-align: center;
    }
    header nav ul li a{
        border-bottom: 1px solid rgba(0, 0, 0, .2);
    }

}
